| Summary: | 碩士 === 義守大學 === 生物技術與化學工程研究所碩士班 === 95 === In recent years, multiple resistances in human pathogenic microorganisms, especially Acinetobacter baumannii and Pseudomonas aerugisosa, have developed and caused serious nosocomial infections. The resent emergence of drug-resistance strains is deeply troubling and highlights the urgent need for new classes of antimicrobial agents. Therefore, the purpose of this study was to evaluate new antimicrobial substances from Chinese herbal medicines.
The preliminary antimicrobial screening of the ethanol extracts from 58 Chinese herbal medicines showed that 31 extracts had antimicrobial activity. Among of the 31 plant extracts, 10 herbal extracts with high efficacies against the test organisms, included the clinical drug-resistant isolates of Acinetobacter baumannii and Pseudomonas aerugisosa, were selected to determine the minimum inhibitory concentration（MIC）by the agar macrodilution method. MIC studies revealed that in range of 1.5 to 20.0 mg/mL are required for growth inhibition in the clinical isolates.
Based on the preliminary antimicrobial screening, Picarpium trichosanthis was chosed for further evaluation of its antimicrobial properties due to it exhibited 100％ inhibition against all of the test microorganisms. The ethyl acetate（EA）fraction of Picarpium trichosanthis displayed antibacterial activity with MIC value at 1.5 mg/mL. Moreover, by using the disc diffusing synergy test, the EA fraction of Picarpium trichosanthis showed synergism effects with the test antibiotics. The results of killing curve and the resistance tests suggested that the extract of Picarpium trichosanthis could be used as a bactericide agent and the test isolates did not induce resistance to the extract. According to the results of GC-MS, the major compounds of the EA fraction, 4-hydroxybenzoic acid and isovanillic acid, were characterized to possess the antibacterial and antioxidant activity, respectively. In which, 4-hydroxybenzoic acid had antibacterial activity with the MIC ranged from 0.75 to 1.0 mg/mL and isovanillic acid revealed antioxidant activity with the IC50 （50％ inhibitory concentration）of DPPH inhibition at 648 ppm. Electron microscopy techniques（SEM）revealed that the extracts had an effect on the morphology of the microorganisms under study. The SEM images provide evidence that the extracts causes swelling of the bacterial body and the disintegration of the cell surface, resulting in cell death.
Overall, these data suggested that the extracts of Picarpium trichosanthis possess substantial antibacterial activity against the clinical drug-resistant Acinetobacter baumannii and Pseudomonas aerugisosa isolates as well as display antioxidant activity, indeed have the potential to be developed into the native antibiotics and antioxidant.
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